1. Field of the Invention
The present invention relates to a method of fabrication of Schottky barrier diodes. More particularly, the invention concerns an improved method of fabricating Schottky barrier junctions having improved barrier height characteristics.
2. Description of the Prior Art
The use of Schottky barrier junctions is well known in the prior art. Thus, a Schottky barrier junction is formed as a rectifying metal-semiconductor junction produced by plating, evaporating or sputtering any of a variety of metals on N-type or P-type semiconductor materials. The commonly used metals are the electrode metals such as molybdenum, tungsten, aluminum, hafnium or aluminum alloyed with copper and the semiconductor most commonly utilized is silicon. The electrical characteristics of such metal to semiconductor junctions are well known to depend upon the work function of the metal as well as the electron affinity of the semiconductor. Further, the energy necessary for an average electron to float in the reverse direction across the barriers is determined largely by the barrier height of the junction, where the barrier height is found to be equal to the difference in work function between the metal and the semiconductor. From this relationship, it follows that an essential requirement of forming a diode junction is that the work function of the metal must exceed the corresponding property of the semiconductor in order that a barrier be present. If this condition is not met an ohmic contact is formed.
Consequently, in the case of aluminum-copper aloyed material it has been found that Schottky barrier diodes can be formed utilizing N-type silicon having a doping less than 8 .times. 10.sup.16 atoms/cu.cm. It is well recognized that tungsten, nickel and molybdenum can be utilized to form Schottky barrier junctions in conjunction with N-type silicon material having the above-mentioned doping; and that hafnium can be utilized with P-type silicon having the above-mentioned doping level to form Schottky barrier junctions.
With the usual aluminum-silicon barrier, a barrier height in the order of 0.68-0.72 electron volts is possible where pure metal exists at the junction after the usual sintering operation employed for faricating the devices.
For many purposes Schottky barrier diodes having a barrier height of 0.68-0.72 electron volts are satisfactory. However, a need exists in the prior art for fabricating Schottky barrier diodes having uniform and significantly increased barrier height.